public class Test {
}
class Solution {
    public ListNode oddEvenList(ListNode head) {
        if(head == null || head.next == null) return head;
        ListNode cur = head;//奇数
        ListNode nH = head.next;//偶数
        ListNode prev = nH;
        while(prev != null && prev.next != null){
            cur.next = prev.next;
            cur = cur.next;
            prev.next = cur.next;
            prev = prev.next;
        }
        cur.next = nH;
        return head;
    }
}